The invention relates to a local communication system comprising a plurality of stations interconnected for the communication of messages via a plurality of serial data channels. The invention further relates to apparatuses for use in such a system.
A system of this type has been described for example by Knapp and Hetzel in a paper "Audio Local Area Network Chip for Cars", presented at the 92nd Convention of the Audio Engineering Society, 24-27 March 1992, Vienna. Knapp and Hetzel propose use of the well known SPDIF format for the transmission of digital audio signals among the various components of a car audio system, and incorporate within that format eight channels for the transmission of control messages in parallel with the audio signals.
In the system of Knapp and Hetzel, known as A-LAN for short, each station (each apparatus) is constructed and configured to transmit on a respective one of the eight control channels, while receiving messages from other nodes on the remaining seven channels.
Some practical problems arise in the implementation of such a system. Firstly, the allocation of channel as described limits the number of stations connected in the ring network. The reference indicates how one might exceed this limit by providing multiple rings, with one of the stations on each ring acting as a gateway to the other ring. Such a gateway is complicated and costly to implement, however, and effectively increases the cost of adding a ninth station in an A-LAN system.
Secondly, each station may find itself obliged to receive unrelated messages simultaneously on several channels. This necessitates costly communication management provisions, for example to buffer and prioritise these messages.
It is an object of the invention to enable the provision of a local communication system as set forth in the opening paragraph, wherein the number of stations connected for the transmission of messages via the data channels is not so strictly limited by the number of data channels, while retaining the benefits of simplicity and low-cost.